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  • Writer's pictureJared Oakleaf

An Interloper, a Captivity Journal, and an Irruption: a mule deer memoir

Updated: Dec 26, 2018

Part 3, of a 3.5 part series on the history of the "youngest" member of the deer family.

Photo by the Author

An Irruption:

Most accounts indicate that mule deer were scarce during and after settlement. While all states currently with mule deer were occupied, densities were variable. In example, a 1826-1831 Hudson Bay Company expedition through northern Nevada makes no mention of deer despite hunting trips in areas now regarded as habitat beachheads [10].

A perfect ecological and social symmetry came to pass at the turn of the 20 century. This situation gave rise to a mule deer irruption.

“…Of four hypotheses that may have favored mule deer population increases between the early 1930’s and mid-1960’s, the most likely is that successional changes in deer habitat were primarily responsible. Much evidence shows that woody plants preferred by mule deer markedly increased in mountain valleys and intermountain slopes following settlement.” [10]

The citation above undervalues the effect of the American conservation movement. It is not by accident that the equally persnickety and fragile mule deer boomed as an era of land disposal and exploitation came to an end. Laws, regulations, and policy mandated multiple use and sustained yield of natural resources. Formerly disturbed habitats were allowed to recover. The synergistic effect of a perfect habitat mosaic and game laws, gave rise to record levels of mule deer.

The mule deer irruption became a cause for concern. The species began to cause noteworthy damage to its own habitat. Many know Aldo Leopolds essay: Thinking Like A Mountain, but few remember that it is as much about deer as it is about wolves.

“…. I have seen every edible bush and seedling browsed, first to anemic desuetude, and then to death. I have seen every edible tree defoliated to the height of a saddlehorn. SUCH A MOUNTAIN LOOKS AS IF SOMEONE HAD GIVEN GOD A NEW PRUNING SHEARS, AND FORBIDDEN HIM ALL OTHER EXERCISE [emphasis added]. In the starved bones of the hoped-for deer herd, dead of its own too-much, bleach with the bones of the dead sage, or molder under the high-lined junipers. … I now suspect that just as a deer herd lives in mortal fear of its wolves, so does a mountain live in mortal fear of its deer.” (Leopold, Thinking Like A Mountain, 1949)[11]

Mule deer exceeded their capacity across much of their range during this irruption [12]. Game managers found themselves feverishly advocating for doe hunts to reduce populations. It was too late.

When ungulates exceed the capacity of the range, long term habitat damage is the outcome. The offending population level follows and takes a dive. Sometimes the dips show an inverse relationship to the peaks. Biology identifies the situation of habitats limiting populations as bottom-up forcing. Following the irruption, mule deer populations across most of the west have declined.

As mule deer populations dive, an ever expanding human population continues to consume. In turn, habitat loss and fragmentation accelerates negative population trends. Meanwhile, plant communities are less productive for mule deer; a product of a wicked mix of climate change, excessive herbivory, and fire suppression. Also, the prevalence of invasive plants render habitat enhancements more complex. Mule deer recovery is not as simple as repeating the habitat disturbances that led to the 1960s irruption. At some point humans need to stop driving nails into the proverbial coffin of mule deer.

When it comes to managing mule deer relative to habitat capacity, we are likely settling into a “new norm”. The info graphic from Montana FWP [13] demonstrates the importance of public hunting as a tool. Managing in this manner is proactive, but is not easy or cheap. The good news is that public hunting continues to provide an ecological service for mule deer.

Montana FWP Infographic from Dickson, 2016

The graph below depicts the trend in New Mexico mule deer harvest since the irruption [14]. This trendline is representative of west-wide mule deer population trends. I do not need to tell the reader to read this from left to right. Nor do I need to tell them that this trendline forecast the future with grim accuracy. Yet hunters and wildlife advocates tend to provide safe harbor for nostalgia. We compare todays mule deer to a reference period of the past. We are referencing something that cannot exist without action. The financial equivalent of hoping for stocks in K-mart to rebound. Maybe this allows us to abscond ourselves of responsibility. But unlike our Pleistocene ancestors, there is no debate, we are responsible. Our responsibility is not out of blame, instead we are aware and capable of orchestrating change - the obligation of a moral duty.

So what does success look like? Mule deer populations will not explode back to the peaks of 20th century and this isn't something we should hope for, as the habitat that gave rise to the irruption does not exist today. Instead, we should advocate for mule deer to be managed relative to the capacity of their habitat. Public hunting will remain the tool to do so.

Moreover, we are still in control of the trend line. We should support initiatives that restore and protect habitat and migration corridors. I have placed several items in the notes section of this blog (part 3.5) that directs the reader to such efforts. If mule deer range is a proverbial pie, we can’t continue to take slices from it and expect deer numbers to boom. To the contrary, deer numbers will only boom if the habitat pie expands. This is how we will put ‘space’ underneath the population trendlines of the future.

In closing, the existence of mule deer will always track with the success of man-kind. Valerius Geist (1990) predicts an extinction of mule deer. In my mind, such a disaster marks the penultimate chapter to our own prosperity. However, robust mule deer herds is an indication of an evolved yet retro human. People that revere science as much as fiction. A society that manages landscape, not from disaster to disaster, but in recognition of the individual’s role as a temporary steward. So stands the mule deer, a grand indicator of our ability to find, what Leopold (1949) called: peace in our time.

Photo by the Author

Continued in part 3.5, available at:

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